Method and tool for injection moulding

ABSTRACT

Method for injection moulding one or more parts using an injection moulding machine and tool ( 12, 13 ) comprising at least one mould cavity ( 17 ), and a feed system comprising at least one gate ( 18 ) and at least one runner ( 19, 20, 21 ) that is located upstream of the at least one gate ( 18 ). The at least one runner ( 19, 20, 21 ) comprises a at least one moveable wall and the method comprises the step of changing at least one cross-sectional dimension (T, B, H, S or S+ΔS) of the at least one runner ( 19, 20, 21 ) by moving the at least one moveable wall in order achieve at least one of the following: a) to vary a flow rate of material in the at least one runner ( 19, 20, 21 ), b) to apply a holding pressure to material in the at least one runner ( 19, 20, 21 ) and consequently to the at least one mould cavity ( 17 ), c) to compress residue in the at least one runner ( 19, 20, 21 ).

TECHNICAL FIELD

The present invention concerns a method for injection moulding one ormore parts in an injection moulding tool comprising at least one mouldcavity, at least one gate, i.e. a side gate or any other type of gate,and at least one runner that is located upstream of said at least onegate.

BACKGROUND OF THE INVENTION

The following advanced injection moulding methods:

-   a) “Co-Injection” or “Sandwich Injection Moulding” of two different    grades of plastic material, and-   b) “Injection Moulding of Family Parts”, have a considerable    potential to provide decreased costs, less environmental loading,    better utilization of resources and improved part quality compared    to current injection moulding and tool technology.

In the co-injection/sandwich injection moulding method two differentgrades of plastic material form a sandwich structure in the wall crosssections of the injection-moulded part whereby a melt first injectedinto a cavity forms a comparatively thin surface layer, usually called a“skin”, which covers the entire part and at the same time, or shortlyafter, a second injected melt forms a comparatively thick layer withinthe skin, called a “core layer”, see FIGS. 1 a, 1 b and 1 c.

There are two different moulding processes for co-injection:

-   -   Simultaneous co-injection into the cavity of the melt of two        plastic grades using a machine equipped with two complete        injection units, which is the original method, and    -   Sequential co-injection of the two plastic grades into the        cavity using a machine with only one injection unit, which have        the consequence that only so-called “cold runners” can be used        for the feed system of plastic melt in the tool, which contrasts        with simultaneous co-injection where both cold runners and        so-called “hot runners” can be used. Mono Sandwich is the trade        name of the sequential co-injection process shown in FIGS. 1 a ,        1 b and 1 c.

The significance of the word “cold” in cold runners is that the walls ofthe runners may be heated to a surface temperature that is lower thanthe melting point of semi-crystalline polymers or the softening/meltinginterval of amorphous polymers and consequently a thin layer of thematerial will solidify against the surface of the walls in a cold runnerwhen the melt flows through the runner.

Co-injection methods are preferably used either:

-   -   to combine different properties of the two plastic materials in        the injection-moulded part, for instance a surface layer        material that for instance has a desired colour, high UV        resistance and/or gloss and a core layer material that is        reinforced to give the part a high stiffness, or    -   in order to save plastic material costs of the injection-moulded        part by using low-priced materials for the core layer, such as        recycled materials, low specified so-called industrial plastic        grades or freshly produced plastic grades without any additives        or with just small amounts of additives admixed after the        polymerisation.

Injection moulding of family parts means that two or more parts with adifferent shape, size and/or weight are simultaneously moulded inrespective mould cavities in the same tool comprising a plurality ofcavities. The injection times for filling mould cavities of differentsizes, volume and/or shape differ, which means that the holding pressureapplied to the melt has to be activated in the cavities at differentpoints of time.

However, the co-injection or sandwich injection moulding and injectionmoulding of family parts methods are not that well established on themarket as other methods such as “Over-Moulding” and “Gas AssistedInjection Moulding” which methods were introduced at the same time asthe aforementioned methods. One reason for this, and maybe the mainreason, is that an appropriate tool technology not been thoroughlydeveloped ever since these methods were taken into use.

There is a need to eliminate the limitations of current tool and processtechnology, which limitations have probably prevented co-injection andinjection moulding of family parts from increasing their market shares.

The Mono Sandwich process is carried out in a machine with only oneinjection unit, as shown in FIGS. 1 a-1 c . A melt volume 3 that isintended to form the core layer of the final part is first metered intothe injection unit 1. Then, a melt volume 2 that is intended to form athin surface layer of the final part is plasticized in an extruder unitin the machine and metered through the orifice of the injection unit 1to be positioned in front of the melt volume 3. As the screw piston 4 ofthe injection unit 1 begins its stroke, as shown in FIG. 1 b , thesurface material 2 will firstly be injected into the mould cavity 5,whereby a thin layer of the surface material will solidify against thecomparatively cold shaping surfaces of the mould cavity. When thesurface material 2 has been partly injected into the mould cavity 5 andthe screw piston 4 continues making its stroke, the core material 3 willpenetrate into the surface material 2 and press the surface material 2against the shaping surfaces of the mould cavity 5, at the same time asthe core material fills the mould cavity inside the surface materiallayer (as shown in FIG. 1 c ). In this manner, a two-layered injectionmoulded part with a thin surface layer and a continuous andsubstantially thicker core layer encapsulated therein, is obtained.

When injection moulding of multi-layer parts in accordance with any oneof the known co-injection methods, it is usually desired that all crosssections of the part shall have a comparatively thin surface layer ofone surface material and a thicker inner layer of a core material. Whenusing co-injection methods the most optimal volume shares of surfacematerial in relation to core material is about 25/75%. When usingcurrent tools in the injection moulding of multi-layer parts accordingto the co-injection method, these shares of about 25/75% are achievedonly if the parts have a simple and/or symmetrical shape, such as thepart/cavity shown in FIGS. 1 a to 1 c.

FIGS. 2 and 3 show examples of problems, which may arise whenco-injection is used for moulding more complex parts using unsuitablegating into the mould cavity. The melt flow extends in differentdirections from a sprue gate 6 to the outer contour of the mould cavity.If there are different flow distances for the melt and different wallthicknesses of the part between the shaping surfaces of the cavity therewill be a different flow resistance for the multi-layer melt in thevarious flow paths in the mould cavity, which in the co-injectionprocess results in flow fronts for the two plastic melts that arenon-uniform with respect to each other and also non-uniform with respectto the outer contour of the mould cavity. In the parts of the mouldcavity where the flow paths for the melt are substantially longer thanthe flow paths in other parts of the mould cavity, reasonable optimalshares of surface and core materials, respectively, are not obtained inthe cross section at the end of the flow paths furthest from the spruegate 6 where there is only core material 7, as shown at the right-handside of the part in FIG. 2 , which shows the part from above and in across section along the line A-A. It can namely be seen in FIG. 2 , thatthe core material melt 7 has penetrated through the surface material 8at the flow front.

It is possible to partly obtain a multi-layer structure in the parts ofthe mould cavity which have the longest flow paths by overdosing thesurface material melt, but, as can be seen in FIG. 3 , a too largeamount of the surface material 8 is obtained at the end of the shorterflow paths, which means that the core material will not reach the outercontour of the mould cavity at these positions. Furthermore the flowfront of the multi-layer melt will be split when the flow front passesopenings for connections, such as reinforcements 9 or attachment means10 etc. This means that optimal volume shares of surface and corematerials cannot usually be maintained, due to the breakthrough of corematerial and the excess of surface material which are obtained atundesired positions in the product as shown in FIG. 2 , which shows anormal portion of core material in the reinforcements 9 and only corematerial in the snap-action attachment 10. In FIG. 3 , thereinforcements have a too large portion of surface material, and thesnap-action member 10 has a more normal share.

For injection moulded parts, such as panels, covers, housings, knobs,handles etc. there are generally specific demands on the properties ofthe visible surface layer of the parts, such as high finish, specialfeatures such as ultra-violet (UV) and heat resistance, high formaccuracy, freedom from sinking, etc. This means that in case such partsare injection moulded with current methods using only one comparativelyexpensive material, the cost of the part will be fairly high. Forportions of the parts which are not visible when the parts are in usethere are usually no such demands on properties. Features such asconnections, reinforcements and attachments, which have to exhibit goodmechanical properties, such as toughness and rigidity, may have to beinjection moulded using a material which is not suited for portions ofthe part that are visible in use. These types of parts are oftenmulti-layer injection moulded by using the over-moulding method, oftenreferred to as “double moulding”. FIG. 4 shows the part illustrated inFIGS. 2 and 3 injection moulded using the over-moulding method. In thismethod, a material 7 is firstly injected into one mould cavity, whichforms the rear part with the connections 9 and 10, whereupon the cavitythat has formed the upper surface of the rear part is changedautomatically in the over-moulding tool to a cavity which is somewhatlarger, meaning that over-moulding with a surface layer material 8 cantake place as shown in FIG. 4 . However this method results insubstantially high investments in machines and tools and a comparativelylong cycle time.

By overdosing the surface material melt it is possible to obtain amulti-layer structure also in the parts of the mould cavity, which havethe longest flow paths, but as can be seen in FIG. 3 , a too largeamount of the surface material 8 is obtained at the end of the shorterflow paths, which means that the core material will not reach the outercontour of the mould cavity at these positions.

EP 2,035,206 discloses a method and a tool for multi-layer injectionmoulding according to the co-injection method which provides a solutionto the problems outlined above when using conventional tools forco-injection. According to EP 2,035,206 a method for co-injectionmoulding a part incorporating an upper portion of the part and at leastone connection integrated therewith is described. The cavity for the atleast one connection is positioned in a movable tool core, see FIGS. 5 aand b , which core can be controlled to close and to open the entranceof the cavity for the at least one connection. The upper portion of thepart is filled through an appropriate gate, for example a side gate witha plurality of runners upstream of the side gate or through any othersuitable type of gate. When the entrance to the at least one connectionis in a closed position as shown in FIG. 5 a , the cavity for the upperportion of the part will be properly co-injected as the cavity of the atleast one connection will not split the flow front of the co-injectionprocess for the upper portion of the part. When the cavity of the upperportion of the part is completely filled and all metered surfacematerial is used for moulding the surface layer of the upper portion ofthe part, the tool core for the at least one connection is activated toopen the entrance whereby the melt of the core material will breakthrough the surface material layer at the entrance and fill the cavityof the at least one connection, i.e. the at least one connection willconsist of only core material. So, the method according to EP 2,035,206will result in a multi-layer moulded part that is similar to the partshown in FIG. 4 , which is injection moulded by the over-mouldingmethod.

SUMMARY OF THE INVENTION

The object of the invention is to provide an improved method forinjection moulding one or more parts in an injection moulding tool thatcomprises one or more mould cavities and which tool has a feed systemfor the melt, which comprises at least one runner that is locatedupstream of at the least one gate. The gate can be a side gate or anyother type of gate which lets the melt into the at least one mouldcavity. The feed system thus accommodates the melt coming from theinjection unit in the injection moulding machine and guides the melt inone or more runners through the injection moulding tool to one or moregates into one or more mould cavities.

The at least one runner according to the invention comprises at leastone movable wall and the method comprises the step of changing at leastone cross-sectional dimension of the at least one runner by moving themoveable wall to allow at least one cross-sectional dimension of the atleast one runner, such as height and/or width and/or diameter and/or anyother dimension in a cross section with any other shape, to be changed,either manually or automatically before the injection moulding operationstarts, or during an ongoing moulding cycle, to thereby adjust the meltflow rate in the at least one runner and/or to apply a holding pressureto the material in the at least one runner and consequently to the atleast one mould cavity, i.e. to allow a mould cavity-specific holdingpressure to be applied to each mould cavity, and/or to compress residuein the at least one runner. The movable wall is arranged to bemechanically, hydraulically or electrically controlled.

The improved method according to the invention is primarily intended tobe used to increase versatility and cost-efficiency and to decreaseenvironmental loading and utilization of resources concerning

-   -   co-injection of parts with a sandwich structure, i.e. a surface        and a core layer of two plastic materials, by using a        single-cavity or a multi-cavity tool, and    -   simultaneous injection moulding of family parts in a        multi-cavity tool where mould cavities have different size,        shape and/or volume.

A method according to the invention can also be applied to conventionalinjection moulding in order to reduce or eliminate various process andtool imperfections.

The present invention also concerns an injection moulding tool forperforming a method according to any of the embodiments of theinvention. The tool comprises at least one mould cavity and a feedsystem comprising at least one gate and at least one runner that isarranged to be located upstream of said at least one gate. The at leastone runner comprises at least one movable wall that is arranged toenable at least one cross-sectional dimension of the at least one runnerto be changed in order achieve at least one of the following:

-   a) to vary a flow rate of material in said at least one runner,-   b) to apply a holding pressure to material in said at least one    runner and consequently to said at least one mould cavity,-   c) to compress residue in said at least one runner, whereby said    tool comprises means to change said at least one cross-sectional    dimension of said at least one runner.

According to an embodiment of the invention the feed system may comprisea plurality of runners located upstream of the at least one gate,whereby the at least one cross-sectional dimension of the at least onerunner is arranged to be individually variable.

According to an embodiment of the invention the tool comprises aplurality of adjacently arranged gate inserts that are adapted to changethe at least one cross-sectional dimension of the plurality of runners.Each gate insert may be arranged to change the at least onecross-sectional dimension of one runner, whereby the flow front ofmaterial entering a mould cavity via the plurality of runners may beaccurately controlled.

According to an embodiment of the invention the tool comprises heatingmeans to heat the at least one runner to a temperature less than amelting point or melting interval of the material in the at least onerunner.

According to an embodiment of the invention a part of the means tochange the at least one cross-sectional dimension of the at least onerunner constitutes the moveable wall.

According to an embodiment of the invention the movable wall is arrangedto be mechanically, hydraulically or electrically controlled by themeans to change the at least one cross-sectional dimension of the atleast one runner.

According to an embodiment of the invention the tool at least part ofthe means to change said at least one cross-sectional dimension of theat least one runner constitutes an exchangeable cassette that isarranged to be removably attached to the tool. A “cassette” is aprotective case or holder comprising wear-resistant material, such assteel, which will protect its contents from being damaged when the meansto change said at least one cross-sectional dimension of the at leastone runner is being operated, under high pressure for example.

The object is achieved by a method and tool having the features recitedin the claims, which make it possible to

-   -   vary the melt flow rate, cm³ s⁻¹, in at least one runner, and        thereby in at least one mould cavity that is connected to said        runner,    -   apply a holding pressure to the melt via at least one runner,        and thereby to at least one mould cavity that is connected to        said runner,    -   compress the residue in the feed system to a minimum volume in        at least one of the runners in said feed system.

It should be noted that the expression “changing at least one dimensionin the cross section of the runner” is intended to mean that at leastone dimension in at least one part of the at least one runner may bechanged. For example, the height in only one portion of a runner may bechanged and not necessarily the height along the entire length of thatrunner.

The technical term “side gate” means a slot connecting at least onerunner to one mould cavity, which slot is not too narrow and has alength that is appropriate for the spread of melt in the mould cavityconnected to said gate. A side gate may be located to let in the melt ata lateral edge or close to such an edge of either a single-curved or adouble-curved wall or an edge of a straight line of a flat wall of thepart to be moulded. A gate should be dimensioned to allow for asufficient flow of melt to fill the mould cavity without causing a toohigh shear that could degrade the material.

The melt may be any injection-mouldable material, such as any plastic,glass, elastomer, thermoplastic or thermosetting polymers or ediblematter, such as confectionary, or a mixture containing at least one suchmaterial.

According to an embodiment of the invention, the feed system comprises aplurality of runners located upstream of the at least one hate and atleast one cross-sectional dimension of the at least one runner isindividually variable so that the melt flow rate in each of a pluralityof runners can be individually controlled by individually adjusting atleast one cross-sectional dimension in at least one of said runners. Therequired adjustment of at least one movable wall in order to achieve adesired individual flow rate from the outlet of said at least one runneris preferably carried out by hand-operated adjustment of the means formoving the at least one movable wall in the at least one runner.Consequently, the flow front profile and spread of melt in the mouldcavity can be controlled to be even and continuous and the entire flowfront can be controlled to simultaneously or almost simultaneously reachthe contour that is farthest away from the side gate of the mouldcavity.

A method according to the present invention can therefore be used tomould various types of parts that may have a fairly complex design, andespecially when used for co-injection moulded parts the share of corelayer material is increased and more uniformly spread compared to whatis possible with conventional prior art methods of co-injection mouldingusing tools having a conventional feed system. According to anembodiment of the invention it is possible to reach a share of the corematerial which is substantially higher compared to the use ofconventional tools with a conventional feed system. A share of at leastabout 50% of the total volume of a part having a fairly complex shape ispossible to reach without core material melt breaking through thesurface material layer and/or without too much surface materialgathering in certain regions of the part. In case the parts have asimple and symmetric form even higher share than 50% will be reached.

The at least one dimension of a runner may be adjusted to make itpossible to vary the melt flow rate either

-   -   manually before start of the moulding operations by means of a        screw device, in a stepless manner by an amount that is fixed        during the entire moulding operations, or    -   automatically, for example during an ongoing injection moulding        cycle, in a stepless or gradual manner by means of mechanics or        hydraulics or an electric circuit including a drive unit and a        control system, which drive system might be hydraulic (gradually        variable) or electric with servo motors (steplessly variable).

The method according to the invention can be used for balancing/finetuning melt flow between cavities in multi-cavity tools or adjustingmelt flow when needed in other injection moulding cases such as mouldingof family parts. Using an electric servomotor as a drive unit provides aversatile and rapid variation of motion and force of the moving core insaid runners whereby controlling of both melt flow and holding pressureoperations can be performed during an ongoing moulding cycle.

According to an embodiment of the invention, a holding pressure can beapplied to the melt in one or more of the plurality of runners wherebythe pressure is momentarily transferred into the, or each respectivemould cavity via the gate that connects the mould cavity with saidrunners. A holding pressure is always, in all injection mouldingmethods, applied in the melt to ensure that the melt in the mould cavitystays densely packed while it solidifies. Said holding pressureoperation according to the present invention is individually controlledfor each of one or more cavities, which can be expressed “mouldcavity-specific”, and the holding pressure operation is initiated at thesame point of time, or substantially at the same point of time, asfilling melt into each of the one or more mould cavities has beencompleted, also called volumetric filling. The injection mouldingmachine's holding pressure function is not thereby utilized. Instead,the injection moulding cycle in each mould cavity comprises:

-   i) using the injection moulding machine's injection function, which    is improved by using the method and tool of the present invention    since this allows the flow front to be controlled individually in    each runner, and-   ii) applying a mould-cavity-specific holding pressure rather than    the injection moulding machine's holding pressure function, whereby    the injection moulding machine is reset as regards pressure, speed    and starting point once each mould cavity has been filled.

When injection moulding family parts, the tool comprises mould cavitieswith unequal size, volume and/or shape that have to be filled usingdifferent injection times, which means that the holding pressureoperation has to be initiated at different points of time in the variousmould cavities.

Applying a holding pressure to the melt in one or more of the pluralityof runners may be achieved by mechanical means with a drive unit that iscoupled to a moving package/row of gate inserts and/or coupled to movingcores in a plurality of runners in the feed system upstream of theplurality of runners or upstream of any other chosen type of gate intothe mould cavity. The mechanics and drive systems that are used forvarying melt flow in said runners can as well be used for applying aholding pressure to the material in the runners and consequently to therespective mould cavities. The mechanics and drive system have to beadjusted so that enough volume of melt can be accumulated in therunners, constituting a so-called melt cushion, by moving backwards thepackage/row of gate inserts and/or the cores in one or more runnersupstream of said gate inserts, which melt cushion ensures that the drivesystem pressurizes the melt during the whole holding pressure time.

A device for shutting off the melt flow upstream of runners wherein aholding pressure is intended to be applied, has to be arranged toprevent a portion of the melt in the melt cushion from flowing backwardsin said runners thereby avoiding that a desired holding pressure wouldnot be reached. It should be noted that the force needed for applying aholding pressure in some cases has to be higher than the force neededfor changing the melt flow rate in the runners. The speed needed to moveinserts and/or cores when changing the flow respectively applying aholding pressure are usually different as changing the flow usually is amore rapid movement. Thus, when combining the operations of changingmelt flow and applying a holding pressure in the same runner during thesame moulding cycle the dimensioning and specifications of the mechanicsand the drive system have to be adapted to the force and speed neededfor both operations.

This method according to the invention is especially intended to be usedfor single-material injection moulding family parts in a “multi-cavitymould”, i.e. a tool comprising a plurality of mould cavities, where twoor more cavities are different regarding shape, size and/or volume andwhereby the cavities are only partly simultaneously filled as cavitieswith a large volume need a longer time to be filled than cavities with asmaller volume.

Accordingly the feed system for injection moulding family parts shouldcomprise means for:

-   -   a mould cavity-specific holding pressure function, operating        individually in the melt in each cavity, and    -   a shut-off device upstream in the runner(s) of said holding        pressure function to prevent backflow of the melt when the        holding pressure operation is activated.

Hereby the moulding process for the part in each separate mould cavitywill turn out practically as if the part has been separately mouldedwith conventional methods, as whereby each part's weight and quality,such as surface finish, shape accuracy, mechanical properties etc. willremain unchanged.

The present invention is not limited to be used for co-injectionmoulding and/or injection moulding of family parts, but may also forinstance be applied to single-material injection moulding, with one ormore equal mould cavities, and to multi-material over-moulding.

The tool and method according to the invention can preferably be used incertain cases of conventional methods of injection moulding, for examplein cases where the time for plasticizing and metering is so long thatthe time for performing the total moulding cycle has to be lengthened.By using the tool and method according to the invention, plasticizingand metering can start as soon as the mould cavity-specific holdingpressure operations have been initiated, thus making it possible toshorten the cycle time.

According to an embodiment of the invention, compressing the materialresidue in the feed system can substantially reduce the amount of to berecycled either by grinding and plasticizing the residue directly in theinjection unit of the machine or by separate recycling. Residue in oneor more runners upstream of the plurality of side gate runners can becompressed either in case the compressing operation is combined with aholding pressure operation, or by a separate compressing operation incase a holding pressure operation is not used in said one or morerunners. In the first case, i.e. combining with a holding pressureoperation, a minimum of residue after compressing the residue in saidone or more runners is reached by adjusting the melt cushion to containa volume of melt that is exactly, or slightly larger than the volumethat is needed for the holding pressure operation whereby a pressureshould be applied to the melt during the whole duration of the holdingpressure operation. The moving and pressurizing cores in said one ormore runners will then compress the mixture of solidified and moltenmaterial residue to a minimum volume. In case the cores in said one ormore runners are used merely for varying the melt flow rate, acompressing operation can be performed when the injection operation hasceased just by switching over the control system to a speed, pressureand/or time that is/are appropriate for the compression operation insaid one or more runners. It should be noted that the degree ofreduction of the residue in the feed system by compressing is dependantof factors such as stiffness, melt viscosity, reinforcement etc. of themixture of molten and solidified material and the temperature of thewalls in the runners.

A method for compressing the residue in the plurality of runners is alsooffered according to the invention by combining the embodiment of twopackages/rows of gate inserts assembled opposite each other on bothsides of the parting line of the tool and each of them coupled to adrive unit, whereby the compressing and holding pressure operations areperformed simultaneously directly after volumetric filling of thecavity. The gate inserts in the package/row of inserts have to beadjusted so that the compressed residue will become as thin as possiblewithout colliding with inserts on the opposite side of the parting line.

According to an embodiment of the invention the method comprises themeans of heating the at least one runner to a temperature less than amelting point or melting interval of the material in the at least onerunner. This can be achieved by heating a tool insert where the runneris positioned, to a temperature that is substantially higher than mouldtemperatures recommended by plastic material producers. The plasticlayer, often called the “skin”, of the melt that solidifies against thesurface of the at least one runner will become extraordinarily thin. Thehigher the temperature on the heated surface, the thinner the thicknessof the skin will become. Heating the tool inserts is performed by usinga separate heating unit and the inserts must be thermally insulated toprevent heat being conducted or radiated to other parts of the tool,such as mould plates, mould cavity inserts etc. The designation of sucha runner is still “cold runner” as its wall surface temperature is lowerthan the melting point or melting interval of the material meaning thata skin will solidify against the surfaces in the runner.

The embodiment of heated runners is primarily provided to ensure thatthe melt cushions in the runners will contain the highest possible shareof molten material so as to achieve an efficient holding pressureoperation. Flow resistance and shear in the melt will become lower aswell which means that a lower injection pressure is needed for fillingthe melt through runners and into the mould cavity, which could befavourable when flow paths are long and/or flow resistance in the mouldcavity is high.

All thermoplastic injection moulding grades, amorphous as well assemi-crystalline, and also thermoelastic grades, can be used with theembodiments according to the present invention. High viscosity amorphousthermoplastic grades such as PC (polycarbonate), PSU (polysulfone) andPES (polyether sulfone) will flow more easily in runners that are heatedto a higher temperature, whereas an increase of injection speed and/orpressure will have less influence. The flowability of thermoelastomers,such as SEBS, is improved by a high shear in the melt. Suchpolymer-specific processing properties for certain plastic materialsindicate that there is a need for runners to be separately heated andfor the cross-sectional area of the runners to be adjusted when tryingto find a process that provides a robust melt flow in the runners.

Generally, plastic materials with special processingproperties/requirements such as high viscosity, high reinforcement, heatsensitive melt, highly shear-dependent flowability etc. could be betterperformed in injection moulding by utilizing one or more embodiments ofthe invention compared to the use of current technology for melt feedsystems in the tool. Embodiments for runners upstream of the side gateare mainly characterised by

-   a) being so called “cold runners”, whereby, in contrast to so called    “hot runners”, the flexibility and reliability to adapt the feed    system to various processing requirements of the plastic material to    be used, as exemplified above, will improve,-   b) having a flow resistance that can be decreased or increased    -   either by infinitely adjusting (increasing or decreasing) their        cross-sectional area,    -   or by separate heating or cooling of the tool inserts in which        the runners are positioned, i.e. these tool inserts are        thermally insulated from the other parts of the tool. When        increasing the cross-sectional area and/or the temperature of        the walls in the cold runners the “open” cross-sectional area        within the solified skin thus will increase and thereby the flow        resistance in the runners will decrease.

Costs, environmental loading and utilization of resources in currentinjection moulding operations can be decreased by implementing a tooland method according to the present invention. The benefits fordifferent injection moulding applications are:

-   a) co-injection moulding:    -   a 10-20% saving of the total plastic material cost for the parts        by using low cost plastic materials, such as recycled grades, in        the core layer, compared to conventional single-material        injection moulding with only the usually more expensive surface        layer materials,    -   decreased environmental loading by using recycled plastic        materials,    -   shorter cycle time, meaning increased production capacity, when        using the Mono Sandwich method in cases where the time for        plasticizing/metering of core material moving the extruder forth        to and back from the injection unit and plasticizing/metering of        the surface material, is so long compared to the specific cycle        time needed for the moulding operation in the cavity that the        total cycle time has to be lengthened,    -   decreased tool costs and a shorter cycle time compared to the        over-moulding method,-   b) injection moulding of family parts:    -   about 30% savings of total purchase price for a family tool        compared to the purchase of separate tools for each of the        family parts,    -   decreased production costs as acquisition and maintenance costs        for the machine and peripheral equipment and costs for occupied        factory area and operators will be lower,    -   decreased utilization of resources, such as steel material and        various components for the tools,-   c) other conventional injection moulding cases:    -   shorter cycle time, meaning increased production capacity, when        the time for plasticizing/metering of plastic material is so        long that the total cycle time has to be lengthened,    -   improved reliability of filling balance in a multi-cavity tool        where the cavities have equal shape, size and volume, meaning        lower risk for not completely filled parts.

Any one or more of the features that are described with reference to themethod according to the invention also apply to the tool according tothe invention, and vice versa.

According to an embodiment of the invention the tool constitutes anexchangeable cassette, comprising one or more features of the tool,which is arranged to be removably attached to the injection mouldingtool, using any suitable fastening means. Any part(s) of the tool, suchas any or all parts of the melt flow varying and pressure-applying meansmay be housed in such a removable cassette.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will hereinafter be further explained by means ofnon-limiting examples with reference to the appended schematic figureswhere;

FIGS. 1 a-c show the Mono Sandwich method according to the prior art,

FIGS. 2 & 3 illustrate some of the problems that can occur wheninjection moulding a part having a complex form using any co-injectionmethod according to the prior art,

FIG. 4 shows the part illustrated in FIGS. 2 and 3 that has beeninjection moulded using the over-moulding method according to the priorart,

FIGS. 5 a-b illustrates a part incorporating an upper portion which isco-injection-moulded and at least one connection integrated therewithwhich is filled only with core material using a method according to theprior art,

FIGS. 6 & 7 show features of a tool according to an embodiment of theinvention,

FIG. 8 shows a feed system according to an embodiment of the invention,

FIG. 9 shows a plurality of runners,

FIGS. 10 a-d shows means for changing a cross-sectional dimension andfor applying a pressure in the melt in a plurality of runners accordingto an embodiment of the invention,

FIGS. 11 a-c shows means for changing a cross-sectional dimension andfor applying a pressure in the melt in a plurality of runners accordingto an embodiment of the invention,

FIG. 12 is a flow diagram showing the steps of a method according to anembodiment of the invention.

It should be noted that the drawings have not necessarily been drawn toscale and that the dimensions of certain features may have beenexaggerated for the sake of clarity.

DETAILED DESCRIPTION OF EMBODIMENTS

FIGS. 6 and 7 show the two halves of an injection moulding tool, onehalf 12 on the stationary side and the other half 13 on the moving sideof the clamp unit of the injection moulding machine in which the tool ishoused, and which tool may be used in a method according to the presentinvention, such as any co-injection method and the method to mouldfamily parts. The illustrated tool halves 12 and 13 comprise athree-plate mould in which a stripper plate 14 constitutes the thirdplate. A beam 15 mounted on the stripper plate 14 comprises side gateinserts 16 or 26, and which beam 15 and side gate inserts 16 or 26 aredetachable from the stripper plate 14.

The tool halves 12 and 13 comprise two mould cavities 17 in which theparts are to be formed and each mould cavity has a side gate 18. Thetool halves 12 and 13 also comprise tool inserts 25 where a plurality ofside gate runners 19 and a plurality of two branch runners 20 and a mainrunner 21 are positioned.

In the illustrated tool halves 12 and 13 of FIGS. 6 and 7 , said runners20 and 21 have rectangular cross sections and are completely positionedin tool inserts 25 mounted on the moving side tool half 13 and the topsurface of the moving cores (40 in FIG. 11 c ) is located at the bottomof the runners 20 and 21, the walls of the through-hole for the movingcores 40 are the side surfaces of said runners and the flat or curvedsurface of the mould plate 12, opposite inserts 25, in the stationarytool half is located at the top surface of said runners.

FIG. 11 c shows that, according to an embodiment of the invention, theplurality of branch runners 20 and main runners 21 may have asubstantially circular cross-section, a substantially oval cross-sectionor any other geometry. By setting the height Sx on the axis of symmetryof the cross-section of the runners 20 or 21 as shown in FIG. 11 c thecross-section could, if desired, become substantially oval. Features ofsaid runners 20 or 21 with a substantially circular or an oval crosssection are firstly that the plastic residue in the runners 20 and/or 21will have a smaller volume at the same flow resistance thancorresponding runners with rectangular or square cross sections,secondly that the groove 43 together with the radially shaped surface ontop of the core 40 forms a flange 44 that will press against the surfaceof the through-hole for the cores 40, and, especially when a highpressure is built up in the melt or an extreme low-viscosity plasticmelt is used, this design of the top of the core will contribute to animproved tightening in order prevent leakage of melt between the core 40and its through-hole in the tool insert 25.

The tool halves 12 and 13 in the FIGS. 6 and 7 are merely an example ofan injection moulding tool which may be used with the method accordingto the present invention. Generally, a tool does not necessarily have tocomprise a stripper plate 14 and a beam 15. Side gate inserts 16 and 26or cores 40 associated with a plurality of runners 19, 20 and 21, asshown in FIGS. 9, 10 a-d and 11 a-c, no matter if they are coupled todrive mechanics according to the invention or not, can be positioneddirectly in the stationary half 12 as well as in the moving half 13 ofthe tool. A tool according to the present invention may also compriseany number of mould cavities 17, such as one, two, three, four, five, ormore mould cavities, where, in the case of a plurality of mould cavitiestheir shapes, sizes and/or volumes may be the same or different.

FIG. 8 shows features of a feed system according to an embodiment of theinvention which is used to feed plastic melt into one or more mouldcavities 17 (not shown in FIG. 8 ) when the injection moulding tool isin use. When the injection moulding tool is in use, there is namelyplastic material in the main runner 21, the two branch runners 20 andthe plurality of five or two streamlined side gate runners 19. The sidegate 18 supplies the melt to the cavities 17. FIG. 8 thus illustrates anexemplary shape and geometry of said side gate 18 and said runners 19,20 and 21. The feed system is situated in the parting line of the toolin between the moving half 13 and the stationary half 12 and the beam15. The plastic material in the feed system shown in FIG. 8 has nocompressed portions or any other deformations, so the shape/geometry ofthe plastic material fully corresponds to the surfaces/geometry of therunners and side gate of the feed system in the tool.

The term “gate” means an opening connecting at least one runner to amould cavity. A side gate is an example of such a gate. A side gate maybe located to let in the melt at a lateral edge, or close to such anedge, of either a single-curved or a double-curved wall of the mouldedpart. A side gate is of course also possible to locate at a straightedge of a flat wall of the part such as the side gate 18 into the largercavity 17 shown in FIGS. 7 and 8 . A gate is dimensioned to allow forsufficient flow of melt to fill a mould cavity without causing too highshear and degradation of the material. Only one gate 18 per mould cavityis preferable to avoid weld lines, when the melt is spreading out in themould cavity 17, and other defects in the final part. A plurality ofrunners 19 according to the invention can be arranged to feed meltthrough a side gate 18. A branch runner 20 with its extension alongsidethe inlets to the plurality of side gate runners 19, has to be arrangedto feed the melt into this plurality of runners 19, whereby means, suchas the wedge-like tip 52, to axially split the melt flow front at theinlet of each runner 19, and then deflect the split portion of the meltinto each runner of the plurality of runners 19, which deflection can befacilitated by machining a cross section enlargement 53 partly at theinlet of each runner.

The main runner 21 and the two branch runners 20, shown in FIG. 8 , bothhave a rectangular cross section, with heights Hx and widths Bx. Incorresponding runners with substantially circular or oval crosssections, the diameter is Sx for a circular cross section as shown inFIG. 11 c and the width and height for an oval cross section is Sxrespective Sx+ΔSx. The plurality of runners 19 have a thickness Tx intheir cross section across the melt flow direction. The index “x” meansthat the dimensions Hx, Bx, Sx and Tx belong to more than one of theplurality of runners and thereby may have different, fixed or adjustablesizes. In the illustrated tool, H₁, H₂ and H₃ are the heights of themain runner 21 and of each of the two branch runners 20 respectively,and these heights may have been set by moving the cores 40 either to afixed position in each runner before the injection moulding operationsstarts or to be changed gradually or stepless for each cycle during theinjection moulding operations. The dimensions Tx for the “thickness” ofrespective runners in the plurality of runners 19 are T₁, T₂, T₃, T₄ andT₅ for the large cavity 17 and T₆ and T₇ for the small cavity 17 andeach of the runners 19 may be set at different thicknesses by moving theside gate inserts 16 with the set screws 35, see FIGS. 9 and 10 a.

The tool according to an embodiment of the invention is arranged tocarry out the one or more of the following functions:

-   -   to infinitely variably adjust the melt flow rate, cm³ s⁻¹, to        fill either a single mould cavity 17 or to fill each mould        cavity of a plurality of mould cavities 17 using individual melt        flow rates, and/or    -   to apply a holding pressure in the melt in a single mould cavity        17 or individually in each mould cavity of a plurality of mould        cavities 17, and/or    -   to apply a pressure in the melt to compress the plastic residue        in the plurality of runners 19, 20 and 21 of the feed system so        that a minimum volume of plastic is left inside the runners 19,        20 and 21.

These means are:

-   -   a plurality of side gate runners 19 located upstream of a gate        18, (see FIG. 8 for example), whereby the runners 19 according        to the invention are associated with a plurality of infinitely        adjustable gate inserts 16 or 26 in one of the tool halves and a        fixed gate insert 34 in the other tool half (as shown in FIG. 9        ), or adjustable gate inserts 26 in the other tool half (as        shown in FIG. 10 d ), which plurality of runners 19 can be        coupled to    -   drive mechanics (as shown in FIG. 10 a ), where one or more of        the gate inserts 16 (or inserts 26 in FIG. 10 d ) are coupled        via set screws 35 to an upper wedge 22 and a lower wedge 23 with        a connection 45 to a drive unit (not shown).    -   a plurality of branch runners 20 and main runners 21 (as shown        in FIG. 8 ), where a moveable wall of each of the runners 20 and        21 is constituted by the top of the cores 40 that are moving in        through-holes in the inserts 25 (as is illustrated in the        example in FIGS. 11 a and 11 b ), a portion of the surface of        the through-holes and a usually single-curved surface in the        tool half on the opposite side, and mechanics according to the        invention for the plurality of branch runners 20 and/or main        runners 21 (see FIGS. 11 a and 11 b )    -   which mechanics for each runner of the plurality of runners 20        and 21 may be either infinitely adjustable to set the cores 40        in an optional fixed position, before the injection moulding        operations starts, with a height Hx (as shown in FIG. 8 ) or Sx        (as shown in in FIG. 11 c ) or Sx+ΔSx in an oval cross section,        giving a cross section area in each of the plurality of runners        20 and/or 21 so that a desired melt flow rate through each of        said runners is obtained, or    -   which mechanics for each runner of the plurality of runners 20        and 21 is used for varying the melt flow rate individually in        each of said runners during each cycle of the injection        operations, or for applying a holding pressure operation in the        melt individually in each of said runners, or applying a        pressure in the melt to compress the plastic material to a        minimum volume individually in said runners corresponding to the        heights Hrx or Srx, or for sequentially combining said melt flow        adjusting operations and holding pressure operations during the        same moulding cycle. The index “r” means “residue”, i.e. the        plastic material remaining in the plurality of runners 19, 20        and 21 after the, or each mould cavity has been filled (see        FIGS. 10 d and 11 c ).

FIG. 11 c illustrates a holding pressure operation where a substantiallycircular cross section of a runner 20 and/or 21 expands from a height Sxto Sx+Sex in order to accumulate a melt cushion that is necessary forthe holding pressure operation. At the end of the holding pressureoperation, (see the drawing on the right in FIG. 11 c ), the meltresidue in the runners is compressed to a height Srx=about 0.6 Sxprovided that the initial cross section is substantially circular with adiameter Sx.

The plurality of runners 19 upstream of the gate 18 may be used merelyto adjust the melt flow individually in each runner 19 and thereby theprofile of the melt flow front can be formed to spread in thecavity(-ies) 17 in such a way that optimum filling is obtained. Thedimension Tx is, by successive trials, individually set in each runnerof the plurality of runners 19 until the melt flow front in the mouldcavity has obtained a desired profile and the entire flow front willreach the farthest contour of the mould cavity at practically the sametime. FIG. 9 shows a plurality of gate inserts 16 mounted in a recess 32of a cassette 33, which inserts 16 together with the fixed insert 34 inthe tool half on the opposite side form a plurality of runners whereeach runner can be adjusted individually by the set screws 35 to adimension Tx in the plurality of runners 19. The cover screws 36 have tobe unscrewed before the set screws 35 can be turned. The cassette 33 andthe fixed insert 34 are easy to mount and dismount in the stationary ormoving mould plates of the tool.

The embodiment exemplified in FIG. 9 can be used in tools where there isa need of

-   -   an optimum flow front profile for the spread of melt in the        mould cavity, for example at co-injection or conventional        single-material injection moulding of parts with complex design,    -   optimum spread of the melt in a mould cavity combined with        balancing the melt flow among mould cavities with equal shape,        size and volume in a multi-cavity tool.

The embodiment shown in FIG. 9 can be supplemented with drive mechanicsto apply a force on the gate inserts 16, (see FIGS. 10 a-c ) to performa holding pressure operation in the melt in the plurality of gaterunners 19 upstream of the side gate 18 and consequently a holdingpressure in the melt that has been fed into the mould cavity 17.

In the embodiment shown in FIG. 10 a there is also a cassette 33 with arecess 32 where the side gate inserts 16 are mounted and which togetherwith the fixed insert 34 form a plurality of runners 19 upstream of theside gate 18. The set screws 35 are connected to the upper wedge 22 andthe dimension Tx can be adjusted individually by the set screw 35 ineach gate insert 16 in the plurality of runners 19 so that the meltflow, when having passed the plurality of runners 19, will form adesired flow front in the mould cavity 17.

FIGS. 10 a-c show an example of holding pressure operational steps,where a plurality of side gate inserts 16 are coupled to an upper wedge22 that via a lower wedge 23 has a connection 24 to a drive unit thatmay be a double-acting hydraulic cylinder or a hydraulic motor or anelectric servo motor. The holding pressure operation is activated tostart at the same point of time as the melt filling operation into themould cavity 17 has ceased, or at a point of time shortly before thefilling operation has ceased, meaning that the plurality of side gaterunners 19 that has been set to different dimensions Tx (see FIG. 10 a )in the next step (shown in FIG. 10 b ) the package/row of side gateinserts 16 is controlled to expand a distance Te which distance is thesame for all runners in the plurality of runners 19 as the side gateinserts 16 are in fixed positions in relation to each other after beingset to dimension Tx. The expanding movement Te is carried out by pullingthe lower wedge 23 a corresponding distance backwards in the cassette33. Thereby plastic melt is accumulated in the plurality of runners 19to a so-called “melt cushion”, which will accomplish a volume, as aresult of an appropriately chosen expansion Te, which volume is as largeas, or slightly larger than, the volume of plastic melt needed formaintaining a desired holding pressure in the mould cavity 17 during thewhole holding pressure operation. The compression of the plasticmaterial terminates with different dimensions Trx/See FIG. 10 c ) of theplastic residue in the plurality of runners 19 and which dimensions Trxusually are slightly larger than Tx.

With this embodiment a holding pressure operation can be performed inthe plurality of runners 19, and consequently in the mould cavity 17,provided that there is a device in one of the runners of the pluralityof runners 20 or 21 upstream of the plurality of runners 19 for shuttingoff the melt flow to said mould cavity in order to prevent the meltbeing pressed backwards whereby a desired holding pressure in the meltthat has been supplied to the cavity would not be possible to build up.The shut off device may be positioned in a way that the melt flow can beshut off either in one of the plurality of branch runners 20 or in amain runner 21. FIG. 7 shows two shut off devices 30 that each comprisea mini hydraulic cylinder driving a shut off core that closes and opensthe two branch runners 20. Such a shut off device may be designed indifferent ways.

The embodiment according to the invention that is exemplified in FIGS.10 a-c can be used in tools where there is a need of:

-   -   applying an individual holding pressure and an individual time        for the holding pressure operation in each of the mould cavities        in tools with a plurality of mould cavities 17, for example in a        tool for the injection moulding of family parts,    -   applying a holding pressure in a tool comprising a single mould        cavity or a plurality of mould cavities with equal shape, size        and volume in order to achieve the shortest possible cycle time        in cases where a too long time for plasticizing and metering in        the injection unit of the injection moulding machine would cause        a lengthened cycle time when using the holding pressure function        in a conventional injection moulding machine. Injection moulding        using the sequential co-injection method Mono Sandwich could be        mentioned as such a case where the total time for injection,        holding pressure and cooling operations may be so short that the        total time for plasticizing and metering of the core layer        material and docking of the extruder to the nozzle of the        injection unit, followed by metering of the surface layer        material will cause a lengthened cycle time. With a        cavity-specific holding pressure, the metering of core material        can start as soon as the cavity(-ies) has/have been completely        (volumetrically) filled as the holding pressure operation in the        injection unit of the machine and the corresponding time for        said operation is not used.

The embodiment comprising a plurality of side gate runners 19 andcassette 37 which is shown in FIG. 10 a , comprising the mechanics toapply a holding pressure in the melt, is possible, even without takingdown the tool from the injection moulding machine, by mounting anddismounting the tool in the following way:

-   -   Mounting starts with pushing the cassette 37 into the recess in        between the mould plates 39 with the wedge 23 in the rear        position, (see FIG. 10 b ) and then connecting the coupling 45        to said wedge. The wedge 23 is then pushed forward until it        reaches its end position, (see FIG. 10 a ) and at the same time        the wedge 23 is pushing the wedge 22 within the clearance 50        towards the parting line between the tool halves 12 and 13.        After having mounted the cassette 33 in the mould plate 39, set        screws 35 together with the side gate inserts 16 or 26 (FIG. 10        d ) can be screwed through the inserts 16 or 26 from the parting        line and tightened into the wedge 22. All dimensions Tx of the        plurality of runners 19 are thereby set in their start positions        Tmax, such as 3 mm. Finally the cover screws 36 should be        screwed into each of the side gate inserts 16 or 26.    -   Dismounting is carried out in the opposite way starting with        unscrewing the cover screws 36 from the side gate inserts 16 or        26.

The embodiment shown in FIGS. 10 a-c can be combined with a plurality ofside gate inserts 26 including drive mechanics, (see FIG. 10 d ), whichreplaces the fixed insert 34 shown in FIGS. 10 a-c . The purpose ofsupplementing said embodiment with a plurality of runners 19 includingdriven side gate inserts 26 is to compress the plastic material residuein the plurality of runners 19 to a minimum volume, corresponding to adimension Trx, which dimension may be different from side gate runner toside gate runner, in order to get smallest possible amount of residualmaterial when recycling the residue directly into the injection unit ofthe machine or when recycling the residue separately. The compressionoperation may be carried out simultaneously from both sides of theplurality of runners 19 (see FIG. 10 d ). The plurality of side gateinserts 26 and its drive mechanics according to FIG. 10 d , is designedjust for performing a compression operation on the plastic residue inthe plurality of side gate runners 19 and thereby has to be combinedeither with the embodiment for applying a holding pressure to the meltin said runners 19 according to FIGS. 10 a-c or combined with a holdingpressure operation in the injection unit of the machine. Usually thedimension Tx could be compressed by at least 50%, i.e. the compresseddimension Trx≤0.5 Tx.

The mechanics of the embodiment for the compression operation of theplastic residue in the plurality of runners 19 as shown in FIG. 10 d isidentical to the mechanics of the embodiment in FIGS. 10 a-c forcarrying out the holding pressure operation, apart from the side gateinserts 26, the set nuts 27, the screws 28 and the coil springs 29. Asthe cross sections of the plurality of runners 19 in FIGS. 10 a-c havebeen set to a dimension Tx and the desired dimension of the compressedplastic residue is Trx the set nuts 27 should be turned to move the sidegate inserts 26 to be set at a dimension Tx−Trx from their initialposition where they are fully tightened to the screws 28 which screwsare permanently fully tightened to the wedge 22. The coil springs 29will ensure that the inserts 26, which are connected to a dowel of theset nuts, are returning together with the set nuts 27 when the driveunit is pulling back the wedges 22 and 23. An example of the pluralityof branched runners 20 and main runners 21 according to the invention,all of them being so-called “cold runners” are shown in FIGS. 7 and 8 inthe form of corresponding plastic residues of the feed system. In thetool consisting of the tool halves 12 and 13, FIGS. 6 and 7 , saidrunners have rectangular cross sections and are completely positioned intool inserts 25 mounted on the moving side tool half 13 where the topsurface of the moving cores 40 constitutes the bottom of the runners 20and 21, the walls of the through-hole for the moving cores 40 are theside surfaces of said runners and the flat or curved surface of themould plate 12, opposite inserts 25, in the stationary tool halfconstitutes the top surface of said runners.

The mechanics according to the invention for the plurality of side gaterunners 19 is constituted by an upper wedge 22 and a lower wedge 23connected to a coupling rod 45, which all are mounted in a cassette 37that is pushed into a recess in between the mould plates 39. The upperwedge 22 is, via the set screws 35, connected to the plurality of sidegate inserts 16 or 26, see FIGS. 10 a and 10 d . The mechanics for theplurality of runners 20 and 21, see FIG. 11 a , is also constituted byan upper wedge 22 and a lower wedge 23 connected to a coupling rod 45,which are all mounted in a cassette 37 that is pushed into a recess inbetween the mould plates 39 and the upper wedge 22 via inclined hooks 42and notches 24 coupled to the moving cores 40.

FIG. 11 a shows the mounting of the moving cores 40 in the through-holesin a tool insert 25. Mounting of the mechanics starts by positioning thecassette 37, wherein the upper and lower wedges 22 and 23 are in a fixedposition as shown in FIG. 11 a , a short distance backwards from thevery front of the recess whereupon the cores 40, including the bridgingpieces 41, are pushed into their through-holes so that the hooks 42 willbe situated on the upper surface of the wedge 22 a short distance to theleft of the notches 24. Then the cassette 37 is pushed said shortdistance forward to its very front position whereby the hooks 42 willslide down into the notches 24 and thus the cores 40 are therebyconnected to the upper wedge 22 as shown in FIG. 11 b . Then, in casethe operation of the cores so requires, the coupling 45 can connect thelower wedge 23 to a drive unit for the purpose of either adjusting themelt flow rate or applying a holding pressure in the plurality ofrunners 20 and/or 21 or the coupling 45 can be connected to a screwdevice (such a device 24 can be seen in FIG. 10 a ) for setting theheights Hx or Sx or Sx+ΔSx in fixed but optional positions in saidrunners with substantially rectangular or circular or oval crosssections. The cores 40 have a flat surface on both sides of their lowerpart which surfaces glide against support pieces 47 to ensure that thehooks 42 are fully kept down in the notches 24 during use of the tool.Demounting is carried out in the opposite order, with the upper andlower wedges 22 and 23 in a fixed position (as shown in FIG. 11 a ), andpulling the cassette 37 a short distance backwards etc. The cores 40can, when unfastened, be pulled out from their through-holes.

The functions and operations according to the invention, such as startand stop times and speeds/forces for the drive means coupled to themechanics for the plurality of runners 19, 20 and 21, have to becoordinated and controlled in such a manner that this new injectionmoulding technology can be adapted to specific and different methodsthat can utilize the invention. Typical operations of the injectionmoulding machine and the tool according to the invention, are the startof injection and changing injection speed at different positions for thereciprocating motion of the screw piston in the machine, changing thecross section and closing/opening of one or more of the plurality ofbranch runners 20 or main runners 21, switch-over to holding pressureeither in the injection unit of the machine or in the plurality ofrunners 19, 20 and 21 in the tool and performing the holding pressureand compression operations in one or more of said runners.

The drive means connected via a coupling rod 45 to the mechanicsconnected to side gate inserts 16 and/or 26 and moving cores 40, whichinserts and cores are associated with the plurality of runners 19, 20and 21, may be hydraulic cylinders. Electric servomotors or hydraulicmotors may also be used. The drive means in a tool according to thepresent invention, may be connected to an electronic control system insuch a way that the moulding process in each mould cavity in a tool witha plurality of mould cavities and a plurality of runners, can to a greatextent be individually and variably controlled regarding melt flow rateand operations for holding pressure and/or compression of plasticresidue in the gating system. The start and end positions for moving theplurality of side gate inserts 16 and 26 and the cores 40 during theinjection and holding pressure operations may be set with the screwdevice 51. The control system may either be stationary and integrated inthe injection moulding machine or located externally to the injectionmoulding machine, i.e. the control equipment may be transportablebetween different injection moulding machines.

The tool inserts 25, shown in FIGS. 7 and 10 , may be designed in such away that two functions of the new injection moulding technologyaccording to the present invention will be accomplished, which functionsare

-   -   heating the tool inserts 25 to reach a temperature on the walls        of the plurality of runners 19, 20 and 21 that might be chosen        to be substantially higher than conventionally used mould        temperatures recommended by plastic material producers, and said        heating of the inserts 25 may be performed so that the least        possible amount of heat is conducted or radiated to other parts        of the tool such as mould plates, cavity inserts etc, and    -   wear properties of the tool inserts 25 should be sufficient to        ensure the lowest possible wear in through-holes for moving        cores 40 and in recesses for moving side gate inserts 16 and 26        in the inserts 25 so that the duration of the inserts 25 will be        equal to at least the life time of the tool.

Heating of the tool inserts 25 is performed by using a heating unit thatis separate from the heating unit that tempers the rest of the tool toachieve and maintain a mould temperature recommended by the plasticproducer. The inserts 25 must be thermally insulated to prevent heatfrom being conducted or radiated to other parts of the tool, which isachieved in several ways such as:

-   -   selection of a steel grade with very low heat conductivity such        as stainless steel, and    -   designing the inserts 25 with outer and inner recesses whereby        the air in the recesses will decrease heat conduction through        the material of said inserts.

Moving cores 40 or side gate inserts 16 or 22 perform a reciprocatingmovement under high pressure and high temperature in the plastic melt ateach process cycle and mostly during a long period of time. Theseprocess conditions will cause a fairly high pressure between cores 40and their through-holes and between side gate inserts 16 and/or 26 andtheir recesses. When injection moulding certain types of plasticmaterial, a mixture of air and volatiles from the melt will to someextent force its way out along the moving surfaces of cores/side gateinserts and/or through-holes/recesses. So there might be both mechanicaland corrosive wear on these surfaces. Minor wear could be acceptable onthe moving cores 40 and side gate inserts 16 and 22 as they are cheaperto manufacture and easy to exchange in the tool, but said processconditions require that the tool inserts 25 have to be manufactured froman extremely high hardened and corrosion resistant steel grade such asstainless steel hardened to at least 60 HRC. Moving cores 40 and sidegate inserts 16 or 22 may be manufactured from a material that issomewhat “softer” but still corrosion resistant. The tool inserts 25 canbe manufactured conventionally or using a 3D printing additive methodusing steel powder.

Further modifications of the invention within the scope of the claimswould be apparent to a skilled person.

The invention claimed is:
 1. Method for injection moulding two or moreparts with a different size, shape and/or volume simultaneously using aninjection moulding machine and tool comprising two or more mouldcavities, and a feed system comprising at least one gate and a pluralityof runners located upstream of said at least one gate, wherein saidplurality of runners comprises at least one moveable wall and saidmethod comprises the step of changing at least one cross-sectionaldimension of said plurality of runners by moving said movable wall inorder to achieve at least one of the following: a) to apply a holdingpressure to material in said plurality of runners and consequently tosaid two or more mould cavities, b) to compress residue in saidplurality of runners, whereby said at least one cross-sectionaldimension of said plurality of runners is individually variable. 2.Method according to claim 1, further comprising the step of heating saidplurality of runners to a temperature less than a melting point ormelting interval of the material in said plurality of runners.
 3. Methodaccording to claim 1, wherein said movable wall is arranged to bemechanically, hydraulically or electrically controlled.
 4. Methodaccording to claim 2, wherein said movable wall is arranged to bemechanically, hydraulically or electrically controlled.